Refactor subject conversion in AuditEvent2Trail and enhance SubjectConverterInterface

- Replaced `array_map` with `array_reduce` in `AuditEvent2Trail` for flattening converted subjects.
- Enhanced `SubjectConverterInterface` with a `supportsConvert` method and PHPStan annotations to improve type safety and flexibility.

src/Bundle/ChillMainBundle/Audit/SubjectConverterInterface.php

@@ -11,13 +11,27 @@ declare(strict_types=1);
 
 namespace Chill\MainBundle\Audit;
 
+/**
+ * @template T
+ */
 interface SubjectConverterInterface
 {
     /**
+     * @param T $subject
+     *
      * @return Subject|list<Subject>
      */
     public function convert(mixed $subject): Subject|array;
 
+    /**
+     * Determines whether the given subject is supported for conversion.
+     *
+     * @param mixed $subject the subject to check for conversion support
+     *
+     * @return bool true if the subject can be converted, false otherwise
+     *
+     * @phpstan-assert-if-true T $subject
+     */
     public function supportsConvert(mixed $subject): bool;
 
     public static function getDefaultPriority(): int;